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Ensure fitness for purpose of LNG

Knowledge of the knock characteristics of LNG fuels is crucial for suppliers and traders to provide reliable and efficient products and for the end user to secure optimal engine operations. DNV GL’s experts help pave the way for safe and efficient end use of LNG, thus supporting an open and free market.

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Martijn van Essen

Rene Bahlmann

DNV GL is facilitating the widespread use of LNG as a transportation fuel. Knowledge of the composition of LNG fuels is crucial for suppliers and traders to provide a reliable and efficient fuel, and for the end user to ensure optimal engine operation. DNV GL’s experts support the LNG industry with tools and services to ensure a safe and efficient use of LNG as a fuel.

Substantial variation in LNG quality

LNG is produced at different locations around the world. Due to differences in natural gas sources, production technologies and target markets for the LNG, the composition of the LNG (the ‘quality’) may vary substantially with the geographical origin. Furthermore, the “boil-off” of the volatile components during LNG transport, transfer and storage leads to a change in composition, also known as “LNG aging”. LNG quality aspects must be considered in billing and in assessing the fitness for purpose of the LNG for the end user.

Impact of proper fiscal metering

DNV GL has recently updated the Recommended Practice (RP) for development and operation of LNG bunkering facilities (DNVGL-RP-G105). The RP provides industry guidance on how to perform amongst others quality measurements of LNG fuel supply. This enables the industry to understand the business impact of proper fiscal metering. DNV GL is currently working on new measurement techniques and fiscal metering methods for LNG quality and quantity determination. DNV GL and Veritas Petroleum Services (VPS) cooperate on LNG Fuel Quality testing.

Matching engines and fuels

There is a variety of engine platforms used in LNG-fuelled ships and trucks. It is essential to safeguard the performance of LNG-fueled engines by matching the engines with the expected variations in LNG composition; the right match ensures the fitness for purpose of the LNG supplied. Specifically, the knock resistance of the fuel must be determined unambiguously. The occurrence of knock can severely compromise engine performance, varying from increased pollutant emissions and reduced fuel efficiency to engine failure. The knock resistance of LNG is characterized by a methane number, which is similar to the octane number used to qualify gasoline.

Knock Resistance algorithm

To determine the fitness for purpose of LNG, DNV GL has developed a generic, next-generation method to quantify the knock resistance of gaseous fuels that can serve as an international standard. The predictions of knock resistance for a wide range of fuel compositions has been verified for a lean-burn engine and demonstrates superior performance compared to the traditional methods. Since our method is based on the physical and chemical processes that govern knock, adapting it to new different engines platforms and fuel compositions is straightforward. For instance, together with a group of key customers, DNV GL is currently applying the method to different engine platforms that use LNG as a fuel (truck, marine and CHP engines).

On-line calculator available to assess fitness for purpose for LNG

An online calculator to characterize engine knock for LNG (PKI Methane Number Calculator for LNG) is available on this website. The user simply enters LNG composition input (nitrogen, methane, ethane, propane, n-butane, 2-methylpropane, n-pentane, 2-methylbutane and 2,2-dimethylpropane), and the tool calculates a PKI methane number, which can be matched with the engine specification. We also make dedicated algorithms for a wide range of gas compositions tailored for individual engines upon request; please contact us if you are interested.

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